Loans - Loans by Class Modified as Troubled Debt Restructurings (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014 Loans	Dec. 31, 2013 Loans	Dec. 31, 2012 Loans
Financing Receivable, Modifications [Line Items]
Number of Loans	16	12
Trouble Debt Restructuring [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	4	3	7
Pre-Modification Outstanding Recorded Investment	$ 7,194	$ 3,747	$ 4,172
Post-Modification Outstanding Recorded Investment	7,194	3,681	4,172
Commercial, Industrial, and Agricultural [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	6	5
Commercial, Industrial, and Agricultural [Member] \| Trouble Debt Restructuring [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	1	1	2
Pre-Modification Outstanding Recorded Investment	2,315	132	1,455
Post-Modification Outstanding Recorded Investment	2,315	132	1,455
Commercial Mortgages [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	10	7
Commercial Mortgages [Member] \| Trouble Debt Restructuring [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	3	2	5
Pre-Modification Outstanding Recorded Investment	4,879	3,615	2,717
Post-Modification Outstanding Recorded Investment	4,879	3,549	2,717
Residential Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	0	0
Residential Real Estate [Member] \| Trouble Debt Restructuring [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	0	0	0
Pre-Modification Outstanding Recorded Investment	0	0	0
Post-Modification Outstanding Recorded Investment	0	0	0
Consumer [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	0	0
Consumer [Member] \| Trouble Debt Restructuring [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	0	0	0
Pre-Modification Outstanding Recorded Investment	0	0	0
Post-Modification Outstanding Recorded Investment	0	0	0
Credit Cards [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	0	0
Credit Cards [Member] \| Trouble Debt Restructuring [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans	0	0	0
Pre-Modification Outstanding Recorded Investment	0	0	0
Post-Modification Outstanding Recorded Investment	$ 0	$ 0	$ 0

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Number of financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 33

-URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953676-111524

+ Details

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Post-modification amount of investment in financing receivables modified by troubled debt restructurings.

+ References

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- Definition

Pre-modification amount of investment in financing receivables modified by troubled debt restructurings.

+ References

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